/* mpz_setbit -- set a specified bit.

Copyright 1991, 1993-1995, 1997, 1999, 2001, 2002, 2012 Free Software

Foundation, Inc.

This file is part of the GNU MP Library.

The GNU MP Library is free software; you can redistribute it and/or modify

it under the terms of either:

  * the GNU Lesser General Public License as published by the Free

    Software Foundation; either version 3 of the License, or (at your

    option) any later version.

or

  * the GNU General Public License as published by the Free Software

    Foundation; either version 2 of the License, or (at your option) any

    later version.

or both in parallel, as here.

The GNU MP Library is distributed in the hope that it will be useful, but

WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY

or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

for more details.

You should have received copies of the GNU General Public License and the

GNU Lesser General Public License along with the GNU MP Library.  If not,

see https://www.gnu.org/licenses/.  */

#include "gmp.h"

#include "gmp-impl.h"

void

mpz_setbit (mpz_ptr d, mp_bitcnt_t bit_idx)

{

  mp_size_t dsize = SIZ (d);

  mp_ptr dp = PTR (d);

  mp_size_t limb_idx;

  mp_limb_t mask;

  limb_idx = bit_idx / GMP_NUMB_BITS;

  mask = CNST_LIMB(1) << (bit_idx % GMP_NUMB_BITS);

  if (dsize >= 0)

    {

      if (limb_idx < dsize)

	{

	  dp[limb_idx] |= mask;

	}

      else

	{

	  /* Ugh.  The bit should be set outside of the end of the

	     number.  We have to increase the size of the number.  */

	  dp = MPZ_REALLOC (d, limb_idx + 1);

	  SIZ (d) = limb_idx + 1;

	  MPN_ZERO (dp + dsize, limb_idx - dsize);

	  dp[limb_idx] = mask;

	}

    }

  else

    {

      /* Simulate two's complement arithmetic, i.e. simulate

	 1. Set OP = ~(OP - 1) [with infinitely many leading ones].

	 2. Set the bit.

	 3. Set OP = ~OP + 1.  */

      dsize = -dsize;

      if (limb_idx < dsize)

	{

	  mp_size_t zero_bound;

	  /* No index upper bound on this loop, we're sure there's a non-zero limb

	     sooner or later.  */

	  zero_bound = 0;

	  while (dp[zero_bound] == 0)

	    zero_bound++;

	  if (limb_idx > zero_bound)

	    {

	      mp_limb_t	 dlimb;

	      dlimb = dp[limb_idx] & ~mask;

	      dp[limb_idx] = dlimb;

	      if (UNLIKELY ((dlimb == 0) + limb_idx == dsize)) /* dsize == limb_idx + 1 */

		{

		  /* high limb became zero, must normalize */

		  MPN_NORMALIZE (dp, limb_idx);

		  SIZ (d) = -limb_idx;

		}

	    }

	  else if (limb_idx == zero_bound)

	    {

	      dp[limb_idx] = ((dp[limb_idx] - 1) & ~mask) + 1;

	      ASSERT (dp[limb_idx] != 0);

	    }

	  else

	    {

	      MPN_DECR_U (dp + limb_idx, dsize - limb_idx, mask);

	      dsize -= dp[dsize - 1] == 0;

	      SIZ (d) = -dsize;

	    }

	}

    }

}